Hi all,trying to help my mom out... she has a brand new 2014 coachmen ... its a 27' class C on a E450 Chassis V-10i found these.. 18' flex panels... for $99 ea.!!! Sun electric has them for $76!!!I was thinking two... now i need an MPPT controller to use to change the voltage to 12v... my question is... what is the true wattage convert when charging at 12v, or is it charging at a higher amp rating... a little confused I be.... and i haven't even started the Cider yet.. lolwhats a good true MPPT controller to use...

If those panels work out I recommend the 20 amp Rogue controller $250 to get the power to the batteries.

i saw that one... is it too much trouble to deal with the 24v to 12v?

You can't use the $102 Eco-Worthy MPPT controller because it can't accept that 46Voc voltage input. Is more like 42v limit. Next up in price would be a Tracer MPPT at around $140 that does have the voltage (100v) but IMO you should keep the voltage well below that to be sure. Which means put the 46v Voc panels in parallel not series. Others might say go two in series at 92Voc but pushing your luck IMO. Same with any other controller with 100Voc limit.Next up in price is probably to near $300 but might have a few extra features. But would your mum ever use those extra features?

I like that idea for ease of installation, but they have a minimum slope of 1:12 listed, and minimum temp for sticking it on of 50 degrees. For a winter install, you put just one 200w rectangular panel made for grid tie (approx. 30 something volts) and get a similar result with less wires and way less real estate gone from the roof. I was advised that the rubber or tpm roof might pull upwards, so I put my panels in with big plastic mounts that hold it off the roof slightly, and allow removal without unscrewing the mount side that touches the roof. But, did have to put the RV sealant in each and every screw hole, of course. I agree with the poster above to get an MPPT controller with a remote. It may not take the place of a shunt type of ammeter/wattmeter, but will give a good idea of what's happening with the batteries. One big panel, or 2 small ones, some cables to cut up, some inline fuses and a switchable circuit breaker might put you a little over $700 in parts, but you will like having the solar always topping up the batteries to the right level. Oh yeah, the stick on panels get very hot, since there's no airspace beneath them. Not sure what that does to the rv roof covering, either, and taking them off to check underneath would likely be difficult.

Do some "serious" research on those flex panels and you will go with something else. I was all gung ho for them, until I did my homework and there is NO way they would end up on my roof.

mom wants solar on her class C.... i need to do this cheap.

dewey02
Explorer II
Dec 27, 2014
The Texan wrote:
Do some "serious" research on those flex panels and you will go with something else. I was all gung ho for them, until I did my homework and there is NO way they would end up on my roof.

I'd like to hear your reasons. (We know that unisolar is out of business.)
Vacay_Wheels
Explorer
Dec 27, 2014
There is a big write-up on the downsides of flexible panels here:

http://www.technomadia.com/2014/11/zephyr-is-solar-powered-800-watt-rv-bus-roof-solar-install/
MrWizard
Moderator
Dec 27, 2014
there are several members HERE , with the Uni-Solar flexible panels
they haven't reported any problems

the panels in those pictures did NOT look like uni-solar flexible panels

they did get more watts per sq ft of space, using framed panels
and the tilt up idea for working on the roof is great
wa8yxm
Explorer III
Dec 27, 2014
bigcitypopo wrote:
i saw that one... is it too much trouble to deal with the 24v to 12v?

That one I can answer: NO trouble at all.. That is what the controller does. The only difference is how you do it, there are a couple ways (Depending on the controller you choose) I am not up on the technology enough to tell you which is best.
rtate
Explorer
Dec 27, 2014
Salvo wrote:
I would avoid mppt if you want to do it cheap.

Get two 12V, 140W panels for $160. The pwm controller costs about $30.

https://www.solarblvd.com/product_info.php?cPath=1_269&products_id=2668

I really dont understand much about solar charging or electricity for that matter.
Would that mean that theoretically these panels would be capable of putting 23.3 amp hours into my batteries? 2×140 watts÷12 volts =23.3 amps.

As a practical matter how many amp hours could you expect to add to your battery bank on an average day?
rockylarson
Explorer
Dec 27, 2014
I think before jumping into the relative merits of the various hardware you should have a clear understanding of what your mom expects from a solar system.
It is not uncommon for a laypersons expectations of a solar installation to far exceed practical limitations.
red31
Explorer
Dec 27, 2014
rtate, I'd use the panel's Isc (8.4A) or Imp(8.0A) with a multiplier of 4 (spring/fall) or 5 (summer) for average day. 8+8 is 16 times 4 is 64 ah/day times 5 is 80 ah/day. Tilting and tracking would yield more.

Different earth locations and time of year yield different multipliers!
CA_Traveler
Explorer III
Dec 27, 2014
rtate wrote:

Would that mean that theoretically these panels would be capable of putting 23.3 amp hours into my batteries? 2×140 watts÷12 volts =23.3 amps.

As a practical matter how many amp hours could you expect to add to your battery bank on an average day?
Divide by 14.0-14.8V where the battery will be charging.

Assuming the panels are flat mounted and depending upon what month of the year and latitude expect 10-15A. On 12/26/14 in Oceanside, CA on a cloud less day I logged 173AH with 750W so you would get about 60AH.
pianotuna
Nomad III
Dec 27, 2014
Hi,

MPPT vs PWM you get about 10% more charging worst case. There is better low light and shade condition charging with MPPT.

However in low wattage systems I'd still go PWM, particularly if over all cost is the driver.
KJINTF
Explorer
Dec 27, 2014

Posted By: rockylarson on 12/27/14 05:47am

I think before jumping into the relative merits of the various hardware you should have a clear understanding of what your mom expects from a solar system.
It is not uncommon for a laypersons expectations of a solar installation to far exceed practical limitations.

Could not agree more

Attached (NOT) instead a link are a few questions I always ask before getting started
I assumed this place allowed a word doc to be posted as an attachment - NOT - Why NOT?

A few things to consider before jumping into a Solar PV equipment purchase / Installation

https://drive.google.com/file/d/0B7h-Gq0lbBefRHpNRXN2U09tWlE/view?usp=sharing